1. Field of the Invention
This invention generally relates to a method of manufacturing a friction member. More specifically, the present invention relates to a method of manufacturing a friction member by mixing powders of copper/tin-contained metal, ceramics and graphite, and performing high-pressure molding and sintering.
2. Background Information
A clutch device of an automobile is fixedly coupled to a flywheel of an engine. The clutch device is primarily formed of a clutch disk assembly and a clutch cover assembly. The clutch disk assembly is formed of a hub coupled to a shaft extending from a transmission, a plate member coupled to the hub for torque transmission, and a frictional coupling member (clutch disk) fixedly coupled to an outer peripheral portion of the plate member. The frictional coupling member is formed of, e.g., an annular plate and friction facings (friction members) fixedly coupled to the opposite surfaces of the plate, respectively. The material of the friction facing can be basically selected from an organic material and a metallic material.
The metallic material is used for heavy vehicles and racing vehicles owing to high resistances of the metal to heat and pressure. The friction facing made of the metallic material is produced by heating and sintering a mixture of predetermined materials to form and fix the facing onto a core plate. The metallic material is primarily formed of a copper powder, and also contains additives such as tin, graphite and ceramics mixed therein. The tin is added for increasing the sintering strength. Graphite is added as a lubricant component for achieving smooth operation properties. Ceramics such as alumina and silica are required as a friction control agent for maintaining and improving a friction resistance and improving a wear resistance.
The conventional metallic friction member described above is molded at a pressure from about 2 MPa to 3 MPa. When such a conventional metallic member is kept at a high temperature of about 300xc2x0 C. or more for a long time, a large amount of tin segregates so that the structure of the friction member is liable to become irregular. A portion containing segregated tin starts melting prior to the other portion. This promotes wear, and therefore tends to lower the friction coefficient.
In view of the above, there exists a need for method of manufacturing a friction member which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
An object of the invention is to manufacture a copper/tin-contained metal friction member having high performance characteristics in which segregation of the tin is suppressed.
According to a first aspect of the present invention, a friction member manufacturing method includes the steps of: mixing powders of copper/tin-contained metal, ceramics, and graphite with each other to form a powder mixture; molding the powder mixture under a pressure larger than 3 MPa to form a molded object; and sintering the molded object. In the method of this aspect of the present invention, since the powder mixture is molded under a pressure higher than 3 MPa, segregation of the tin is suppressed in the friction member even when the friction member is kept at a high temperature for a long time.
According to a second aspect of the present invention, the friction member manufacturing method according to the first aspect further has such features that the pressure for molding is in a range from 3 MPa to about 4 MPa. In the method of this aspect of the present invention, since the pressure for molding is equal to or lower than 4 MPa, drop or the like of the material from the friction member is suppressed.
According to a third aspect of the present invention, the friction member manufacturing method according to the second aspect further has such features that the pressure for molding is in a range from about 3.2 MPa to about 3.4 MPa. In the method of this aspect of the present invention, segregation of the tin is suppressed, and drop or the like of the material from the friction member is suppressed.
According to a fourth aspect of the present invention, the friction member manufacturing method according to any one of the first to third aspects of the present invention further has such features that the graphite is about 50 xcexcm to about 200 xcexcm in particle diameter and 1 to 20% in weight ratio, and said ceramics is about 50 xcexcm to about 200 xcexcm in particle diameter and 1 to 15% in weight ratio.
According to a fifth aspect of the present invention, the friction member manufacturing method according to any one of the first to fourth aspects of the present invention further has such features that the ceramics is made of at least one of a combination of silica, mullite and zircon sand.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, disclose preferred embodiments of the present invention.